1. Field of the Invention
The present invention relates to a track jump on an optical recording and reproducing medium, and more particularly, to a method of performing a track jump without being influenced by a header.
2. Description of the Related Art
Generally, an optical recording medium system, i.e., an optical recording and reproducing apparatus, employs an optical disc as a recording medium and reproduces data recorded on the disc or records data on the disc.
A tracking servo in the optical recording and reproducing apparatus detects a tracking error signal corresponding to a beam tracing state and shifts an objective lens and the body of an optical pickup based on the signal to modify the location of a beam and follow up a predetermined track.
At this time, a track jump is essential to a time search or a variable bit rate (VBR) operation. When the number of tracks to be jumped is small, a track is searched for using a tracking actuator.
FIG. 1 is a block diagram of a typical optical recording/reproducing apparatus capable of performing a track jump. An optical pickup (P/U) 102 makes a light beam focused on an objective lens be put on a signal track on an optical disc 101 under control of a servo controller 106 and focuses light reflected from a signal recording side on the objective lens. Then, the P/U 102 makes the light focused on the objective lens to be incident on an optical detector (not shown) to detect a focus error signal and a tracking error signal.
The optical detector is composed of a plurality of optical detecting devices. An electric signal proportional to the amount of light obtained from the optical detecting devices is output to a radio frequency (RF) and servo error generator 104. The RF and servo error generator 104 detects an RF signal for reproduction of data and a focus error signal FE and a tracking error signal TE for servo control, from the electric signal output from the optical detector. The RF signal is output to a decoder 105 for reproduction, and servo error signals, i.e., FE and TE, are output to the servo controller 106. A control signal for recording of data is output to an encoder 103.
The encoder 103 codes data to be recorded in a recording pulse having a format required by the optical disc 101 and records the coded data on the optical disc 101 through the P/U 102. The decoder 105 reconstructs original data from the RF signal.
A host such as a personal computer may be connected to the optical recording/reproducing apparatus. The host transmits a recording/reproducing command to a microcomputer 111 through an interface unit 110 of the optical recording/reproducing apparatus, transmits the data to be recorded to the encoder 103 and receives the reconstructed data from the decoder 105. The microcomputer 111 controls the encoder 103, the decoder 105 and the servo controller 106 according to the recording/reproducing command of the host.
For the interface unit 110, an advanced technology attached packet interface (ATAPI) unit is typically used. The ATAPI is a specification for interfacing an optical recording/reproducing apparatus such as a compact disc (CD) drive or a digital versatile disc (DVD) drive with a host. The ATAPI is proposed for transmitting data decoded in the optical recording/reproducing apparatus to the host. The ATAPI converts the decoded data into a protocol in a packet format which can be processed by the host, before transmission.
The servo controller 106 processes the focus error signal FE to output a driving signal for focusing control to a focus servo driver 107 and processes the tracking error signal TF to output a driving signal for tracking control to a tracking servo driver 108.
The focus servo driver 107 drives a focus actuator within the P/U 102 to thereby shift the P/U 102 up or down so that the P/U 102 can follow up the rotating optical disc 101 with an up-and-down motion.
The tracking servo driver 108 drives a tracking actuator within the P/U 102 to thereby shift the objective lens of the P/U 102 in a radial direction so that the location of a beam can be modified, and a predetermined track is followed.
When the optical disc 101 is a rewritable disc, particularly, a digital versatile disc random access memory (DVD-RAM), since there is no information on an initial disc, disc control and recording cannot be performed. To overcome this problem, disc tracks are formed on land and grooves to allow information to be recorded on each track, and sector addresses and control information for random access and rotation control are separately recorded on the disc, thereby allowing tracking control to be executed on a blank disc on which an information signal is not recorded. The control information may be recorded in the beginning of each sector by pre-formatting a header area or may be recorded in wobbling shape along each track. The wobbling means that information to be applied to a disc by modulating a certain clock, for example, information on a certain location and information on the rotational speed of a disc, is supplied to the power of a laser diode, so that control signal is recorded at the boundary surface between tracks by a variation of the light beam of the corresponding laser.
For example, in the case of a DVD-RAM, a header area which is pre-formatted at the beginning of each sector is composed of four header fields HD1 through HD4, as shown in FIG. 2(a). The header fields HD1/2 and the header fields HD3/4 are offset from the center of a track in an opposite direction to each other. In other words, the phase of the header fields HD1/2 is reverse to the phase of the header fields HD3/4, and the phase of a tracking error signal detected from the header fields HD1/2 is reverse to the phase of a tracking error signal detected from the header fields HD3/4. In addition, referring to FIG. 2(a), it can be known that the track boundary of a user area in which actual data is recorded has a wobbling shape.
Accordingly, a header mask is put on a header area, as shown in FIG. 2(b), and a track error signal is held during a track servo to prevent deviation from a track center.
To generate a header mask signal indicating a header area, the header area should be detected first.
Various methods can be used for detecting the header area, and one of them is using a wobble signal as shown in FIGS. 2(a) through 2(c).
More specifically, since the number of wobble signals in each sector is fixed, the header area is detected by counting the number of wobble signals. Since a wobble signal may not be detected due to a defect on a disc, the header area is detected by counting clocks, i.e., phase locked loop (PLL)-wobbles, in which wobble signals actually recorded on the disc are subjected to a PLL, as shown in FIG. 2(c), and a header mask signal (H/M) is generated as shown in FIG. 2(b).
For example, PLL-wobble signals are counted starting from a falling point of a previous header mask signal. When a predetermined number has been counted, it is determined that a header area begins, and thus a header mask signal is generated.
Since a wobble signal is not recorded in the header area, no wobble signal is detected from the header area. Accordingly, a wobble is omitted in a header area. When a wobble signal detected is subjected to a PLL without considering the omission of a wobble signal, a PLL-wobble signal elongates. This causes a header mask signal to be generated lagging behind an actual header area, that is, generation of a header mask signal is delayed.
To solve this problem, a PLL-wobble signal is held with a tracking error signal in a header area.
When a track jump command is input, the RF and servo error generator 104 detects an RF signal (shown in FIG. 3(d)) and a tracking error signal TE (shown in FIG. 3(a)) through the P/U 102 in a state in which only a focus servo is on, and simultaneously, the servo controller 106 generates a kick pulse (or a jump pulse) as shown in FIG. 3(c). The kick pulse is applied to the tracking actuator through the tracking servo driver 108. When the kick pulse is applied to the tracking actuator, the speed of the tracking actuator increases, and the objective lens of the tracking actuator is pushed toward a track jump direction by acceleration of the tracking actuator.
At this time, a brake pulse is applied to the actuator at a zero cross point of the tracking error signal for a predetermined brake time to reduce the speed of the actuator. In other words, the tracking actuator is accelerated by the kick pulse and then decelerated by the brake pulse. The brake pulse is an inverted one of the kick pulse and is generated to stably stop the actuator at an exact desired location. When the brake time previously set has elapsed, a tracking servo is turned on.
A track zero crossing (TZC) signal which is turned on/off at the zero cross point of the tracking error signal TE, as shown in FIG. 3(b), is used as a reference signal for determining a kick pulse, brake pulse and a brake on time during a track jump. In other words, the TZC signal is used as a reference signal when determining at what point the brake pulse will be generated after the kick pulse is generated.
When the tracking actuator passes a header area (see the circled part in FIG. 3(a)) during a track jump, the TZC signal may be generated prior to or behind a desired location due to a header, or one more pulse of the TZC signal may be generated as shown in the circled part in FIG. 3(b).
Accordingly, when the optical disc 101 includes header areas like a DVD-RAM, a problem may occur due to a header area during a track jump.
In other words, when the TZC signal is generated prior to or behind a desired location, or when more pulses of the TZC signal than is desired are generated, the TZC signal goes beyond a location where it is originally supposed to be generated, and a kick time, brake time and a servo on time become irregular so that a track jump cannot be exactly and stably performed.
In addition, as shown in FIG. 4(a), when a track jump is performed depending on a track jump command, a wobble signal may not be detected since the tracking actuator crosses tracks.
Since a wobble signal is omitted, as shown in FIGS. 4(d) through 4(g), during a track jump, a PLL-wobble signal elongates. A wobble signal recorded on an actual disc is shown in FIG. 4(d). The part in the circle of FIG. 4(d) is enlarged in FIG. 4(f). The PLL-wobble signal, in which a wobble signal detected as shown in FIG. 4(d) is subjected to a PLL, is shown in FIG. 4(e). The part in the circle of FIG. 4(e) is enlarged in FIG. 4(g). A header area is indicated through an RF signal of FIG. 4(b). The RF signal corresponding to the header area is always higher than a certain level. The RF signal has the same phase with respect to the header fields HD1/2 and the header fields HD3/4.
As shown in FIG. 4(c), a rising point of a header mask signal, that is generated after a track jump, lags behind the actual location of a header area. Consequently, the header area cannot be masked so that a tracking error signal cannot be held in the header area. Accordingly, the tracking error signal becomes larger as shown in the circled part of FIG. 4(a), and the actuator follows up the header.
When the actuator follows up the header, track slippage may occur, and a track servo becomes unstable due to a change in a discrete track error. The unstable track servo deteriorates recording and reproducing characteristics.
In other words, a header area that comes first after a track jump is performed cannot be stably masked so that the system can be unstable due to a header during the track jump.